Fundamental diagrams

As already stated in Sec. 17.3, often speed, flow, and density are not simply plotted as time series, but the relations between them are plotted as so-called fundamental diagrams. Typical fundamental diagrams are speed or flow as the function of density or occupancy. Fig. 27.2 shows the fundamental diagram of flow vs. density obtained from the data of Fig. 27.1. Plausibly, flow is low at low densities (because no vehicle is on the road), and it is low at high densities (because all vehicles are stuck). The behavior in between is however more complex than one maybe would expect, and no complete theoretical explanation is available (35,64,59).

[[Some of this will be discussed in Sec. ]]

Figure 27.2: Fundamental diagram of flow vs. density from the measurements of Fig. 27.1.